1. Field of the Invention
The present invention relates to positive resist composition and a method of forming a resist pattern using the resist composition.
Priority is claimed on Japanese Patent Application No. 2003-314365, filed Sep. 5, 2003, and Japanese Patent Application No. 2004-119495, filed Apr. 14, 2004, the contents of which are incorporated herein by reference.
2. Description of Related Art
In recent years, the level of integration of semiconductor elements has continued to increase.
A multitude of chemically amplified resists that contribute to improved levels of semiconductor element integration have already been proposed.
Japanese Examined Patent Application, Second Publication No. Hei 2-27660 (patent reference 1) discloses a two-component resist comprising, as the principal components, an acid generator, and a base resin in which the hydrogen atoms of the hydroxyl groups of a polyhydroxystyrene, which displays excellent transparency relative to KrF excimer laser light, have been substituted with acid dissociable, alkali dissolution inhibiting groups such as t-boc (tert-butoxycarbonyl) groups.
An outline of the theory associated with resist pattern formation using the type of resist proposed in the above published examined patent application is presented below.
By incorporating t-boc groups within the base resin, the alkali solubility of the base resin is reduced significantly in comparison with the equivalent polyhydroxystyrene containing no t-boc groups. This type of base resin is then mixed with an acid generator, and when the composition is subjected to selective exposure, the acid generated from the acid generator within the exposed portions of the composition causes the t-boc groups to dissociate, thus generating a polyhydroxystyrene, and converting the exposed portions to an alkali soluble state.
Furthermore, (1) Japanese Unexamined Patent Application, First Publication No. Hei 4-287044 (patent reference 2), (2) Japanese Unexamined Patent Application, First Publication No. Hei 5-40342 (patent reference 3), (3) Japanese Unexamined Patent Application, First Publication No. Hei 5-313372 (patent reference 4), (4) Japanese Unexamined Patent Application, First Publication No. Hei 6-130670 (patent reference 5), and (5) Japanese Unexamined Patent Application, First Publication No. 2001-142217 (patent reference 6) propose three-component chemically amplified resist compositions comprising (α) a novolak resin as the base resin component, (β) an acid generator, and (γ) a compound which under the action of acid undergoes dissociation of an acid dissociable, dissolution inhibiting group, thus generating an organic carboxylic acid (namely, a compound in which a carboxyl group has been substituted with an acid dissociable, dissolution inhibiting group).
Patent Reference 1
Japanese Examined Patent Application, Second Publication No. Hei 2-27660
Patent Reference 2
Japanese Unexamined Patent Application, First Publication No. Hei 4-287044
Patent Reference 3
Japanese Unexamined Patent Application, First Publication No. Hei 5-40342
Patent Reference 4
Japanese Unexamined Patent Application, First Publication No. Hei 5-313372
Patent Reference 5
Japanese Unexamined Patent Application, First Publication No. Hei 6-130670
Patent Reference 6
Japanese Unexamined Patent Application, First Publication No. 2001-142217
Patent Reference 7
Japanese Unexamined Patent Application, First Publication No. Hei 10-268508
However, in the technology disclosed in the above patent reference 1, the alkali solubility of the base resin following selective exposure merely reverts to the inherent alkali solubility of the polyhydroxystyrene as the t-boc groups dissociate under the effect of the exposure, and alkali solubility exceeding this level cannot be obtained. Accordingly, the resulting resolution is not entirely satisfactory.
In the three component resists disclosed in (1) to (5) above [patent references (2) through (6)], the action of the acid generated by exposure causes the generation of a carboxylic acid from the component (γ), and the existence of this carboxylic acid enables an alkali solubility of the resist to be achieved that exceeds the inherent alkali solubility of the component (α). Accordingly, the resists display excellent contrast between the exposed portions and the unexposed portions, although the transparency is poor unless the resist film thickness is kept very thin, and the resolution is not entirely satisfactory.
Furthermore, as the level of integration of semiconductor elements continues to rise, resist patterns must not only display levels of resolution capable of resolving the ultra fine patterns targeted by the use of short wavelength light sources such as KrF excimer lasers, but must also enable reductions in LER (line edge roughness) and other defects.
The patent reference 7 listed above proposes a resist material that uses a resin comprising hydroxystyrene units and cyclohexanol units, which has been subjected to cross linking using ether linkages. However, this resist material suffers from defects, and is not particularly satisfactory.
LER describes non-uniform irregularities along the side walls of lines. Defects refer to general problems such as scum and resist pattern irregularities detected by inspecting the developed resist pattern from directly overhead using a surface defect inspection apparatus, such as that manufactured by KLA Tencor Corporation (brand name “KLA”).